Technical Abstract:
Category: methodology improvements
Objective: To identify strengths and weaknesses of commercial Shiga toxin-producing E. coli detection systems and kits in a side by side fashion.
Experimental Design: Three commercial Shiga toxin-producing E. coli detection tests (BAX, GDS, and GeneDisc) and two third party laboratories (IEH and GeneSeek) were compared to the MLG (5B) and USMARC molecular methods for ability to detect top-6 STEC (also known as enterohemorrhagic E. coli [EHEC]). Experiments were performed in two phases. In phase one, beef trim samples of varying sizes were inoculated with low levels (1-3 CFU/sample) of EHEC and detection methods were performed according to the manufacturers instructions or official/referenced protocols. In phase two, 500 beef trim enrichments obtained from a local service lab were divided and tested by each of the seven methods/systems. All samples in phase one and two that were identified as potential positives (stx+, eae+, Top 6 Ogroup+) were then subjected to multiple rounds of culture isolation in order confirm the presence of an EHEC, or to identify the source(s) of the positive screening tests.
Key Results: Used as directed, all methods can detect low levels of inoculated Top 6 EHEC. When single enrichments are divided into the different methods, there is little agreement between methods. One hundred sixty of 500 samples were found to be potential positive by one or more methods, but only 2 samples were positive by all methods. Considering those two samples, one was confirmed to contain an EHEC-O26 and the other a mixture of STEC and non-STEC organisms responsible for the potential positive result.
All methods did identify the one EHEC containing sample.
How this information can be applied in the industry:
This information will allow users of STEC detection tests or systems to draw comparisons and more critically consider the value of a “potential positive” result when multiple organisms may be present. Further, this information can serve as a base line of what number of potential positives different methods may give when put into practice.